Rectifier



Patented Nov. 4, 1947 RECTIFIEB 1 Eric Lidow and Edgar M. Burlin, Los Angeles,

Calif., assignors to Selenium Corporation of America, Los Angeles, Calif., a corporation of California Application July 18, 1944, Serial No. 545,452

Claims. Y 1 This invention relates larly to rectifiers of the dry plate type.

A well known type of dry plate rectifier cornprises a rectifying element in the form of a disc or plate composed of alternate metallic layers constituting electrodes, between which is interposed a rectifying layer of selenium or other substance capable of transmitting electric current in only one direction. In order to conduct current to one of the electrodes, it is customary to provide a resilient conducting member pressed into engagement with the surface of the electrode. The conducting member is usually in the ,form of a radially slotted disc with a centrally dished portion spaced from the electrode, and having radially extending fingers contacting the electrode.v It is important that good electrical contact between'the lingers and the electrode be established in order to maintain low resistance across the rectifier. It is a general object of this invention to establish good electrical contact between the conducting member and the electrode.

After assembly, a rectifier of the foregoing type is usually completely coated with a protective layer of lacquer, varnish or the like, which is applied in liquid form and allowed to dry and harden. During the application of .the coating liquid, it has been found that some of the liquid may enter the radial slots in the yconducting member and seep between the lingers and the electrode, thus impairing the electrical contact. It is, therefore, a principal object of this invention to prevent impairment of the electrical contact by the coatingmaterial, by preventing ingress of coating material between the contacting surfaces.

It is another object of this invention to provide means for substantially closing the slots between the lingers of a resilient conducting member, without affecting the resiliency of the lingers.

It is still another object of this invention to prevent entry of coating liquid between the contacting surfaces of an electrode and a slotted conducting member by superposing a second member over the conducting member to close the slots therein.

It is a still further object of this invention to protect the contacting surfaces of an electrode and a resilient, slotted conducting member against impairment by liquid coating material, by so shaping the electrode that the slots in the conducting member are substantially closed. without impairing the resilience of the conducting member. l

It is still another object of this invention to prevent entry of liquid coating material between to rectiers, and particul the contacting surfaces of` an electrode and a dished and slotted conducting member by providing a second slotted member having fingers closing the slots in the rst member.

This invention possesses many other advantages and has other objectswhich may be made 'more easily apparent from a consideration of several embodiments of the invention. For this purpose there are shown a number of forms in the drawings accompanying and forming part of the present specification. lThese forms will now be described in detail, illustrating the general principles of the'invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best delined by the appended claims.

In the drawings:

Figure l is a top plan View on an enlarged scale of a rectilier incorporating the invention;

Figure 2 is a sectional view taken on line 2--2 of Figure 1;

Figure 3 is afragmentary sectional view similar to Figure 2,V but showing a modified form of the invention;

Figure 4 is a fragmentary sectional View taken on line 4-4 of Figure 3;

`Figure 5 is a top plan View of the device of Figure 3 with parts broken away;

- Figure 6 is a fragmentary sectional view showing another modied form of the invention; and,

Figure 7 is a top plan View of a portion of the device of Figure 6.

Referring to the form of the invention illustrated in Figures 1 and 2, the rectifying element comprises a circular disc composed of a relatively thick metallic base plate' I to the upper surface of which has been applied a thin layer 2 of unidirectional conducting or rectifying material such as selenium, and a second metallic layer 3 of woods metal, or the like, super-imposed on the rectifying layer 2. The upper and lower metallic layers 3 and l constitute what are generally termed front and back electrodes, the front electrode 3 being adapted to be connected to a source of alternating current which is rectified by passing it through the rectifying layer 2. It may be well to note at this point that whereas the rectifying layer 2 and the front electrode 3 are shown in the drawing as being of substantial thickness, in practice these layers are only a few thousandths of an inch in thickness, the back electrode, however, being relatively thick to impart strength and'rigidity to the rectifier.

Electric current is conducted to the iront elec- Erode ,3, by a resilient conducting member, generally designated 4, which is secured to the upper side of the rectifying element, in electrical contact with the front electrode 3, by a machine screw `5 extending through aligned bores in the members. An insulating sleeve 6 surrounds the screw 5 to insulate the latter from the layers I, 2 and 3 vof the rectifying element and also from the conducting member 4. Aterminal lug I is clamped between the head 8 of the screw 5 and the under surface of the back electrode I, and-is insulated from the screw head 8 by a washer 9 of libre or other electrical insulating material. If desired, a metallic washer 4ll) may be interposed between the screw head 8 .and Athe insulating washer 9.

A second terminal lug Il is mounted on the screw l5 in electrical contact with the conducting member 4, the entire assembly of parts being clamped together by a nut I2 threaded on the screw 5. An insulating washer I3 is interposed Abetween the lug I I and the lnut I2, and a metallic lock washer is preferably provided to retain the nut in position.

In order to impart resiliency to the conducting member 4 -and thereby establish and maintain good electrical contact between it and the front electrode 3, the member 4 `is preferably of inverted saucer shape in cross-section and, in the form of the invention depicted in Figures 1 and 2, comprises a pair'of similarly shaped members 20 and 2|, the lower member 2U being nested within the upper member 2l. The lower member 20 includes an upwardly dished -central portion 2li-a and outwardly and downwardly sloping radial finger portions 20b which are separated by radial slots 2li-c (Figure 1), and which are resiliently urged into contact with the front electrode 3 upon assembly of the parts. It Will be observed `with reference to Figure 2 that a pocket 2li-d is formed between the dished central portion 2li-a and the electrode 3.

The upper member 2-I of the conducting member `:1I is so shaped asto fit snugly over the member 20 and have good electrical contact therewith, and comprises an upwardly dished central portion ZI-a and outwardly and downwardly sloping radial nger portions ZI-b separated by radial slots 2I-c. It will be apparent that as the nut I2 iis threaded downwardly on the screw 5, the

outer rim portions of the fingers 2li-b of the member 20 `engage the outer peripheral portion of the surface of the front electrode 3, causing the fingers `to be flexed from their normal inclination. The fingers 2I-b of the upper member 2I are similarly flexed, the resiliency of the fingers of both members establishing and maintaining good electrical contact between the fingers 2li-b and 2 I -b and also between the fingers 2li-b and the electrode 3. A spacing washer I5 of insulating material is interposed between the central portion 2lia of the lower member 20 and the front electrode 3, to limit the downward movement of the nut I2 and thereby predetermine the amount of pressure exerted by the fingers 2lib against the electrode 3.

It is customary to apply a protective coating of varnish, lacquer or the like, indicated at I 6 in Figure 2, over the entire outer surface of the rectifier after it is assembled. This coating is applied in liquid form, and is then allowed to dry and harden. Heretofore, a rectifier of this type included only a single conducting member such as the lower member 20, and it will be apparent that in such case the slots 2U-c in the conducting member provide openings through which the coating liquid may enter the pocket 2li-d and thereafter the more iiuent constituents of the coating liquid may seep between the contact surfaces of the fingers 20-b and the electrode 3. This seepage of coating liquid between the contact surfaces may not only take place outwardly from the pocket k2ll--d, but may also occur lalong the sides of the 'outerportion's 'of the slots. In each instance, it is promoted and facilitated by capillary attraction in the narrow, wedge-shaped space formed between the fingers and the electrode. Upon subsequent hardening, this film of coating material may materially reduce the effective area of contact between the fingers and the 'electrode and thereby adversely affect the operation of the rectifier.

The foregoing 'difficulty is overcome by the instant invention by the provision of the second conducting member 2| overlying the member 20 and oriented about the .axis of the screw 5 into a position wherein the iingers 2rIb of the upper member overlie the slots 20e-cof the .lower .member, as shown most clearly Y.in Figure 1. Conversely., the fingers 2li-b of the `lower member underly the slots 2`I-'-'c of the upper member. It is thus apparent 'that by this arrangement it is possible to provide slotted conducting members, to vobtain the desired resiliency therein, and at thesame time avoid impairment of the electrical contact by causing each slotted member to close the .slots of the other member and prevent coating liquid from Ventering the slots.

If the lower conducting member v2l) is sufiiciently thin, it may suice t'o close the slots 2lic only from above in the manner described, reliance being had on the surface tension of the coating liquid to prevent its entry into the slots through the open outer ends thereof. It has been found, however, that in some instances one or more constituents lof the coating liquid may be of sufficiently low viscosity and low surface tension to enable them to penetrate'the 'open-ended slot-'s from the radially 'outer end 'and then seep between the contact surfaces. To avoid this 'contingency, the upper .member 2| 'may be provided with a, series of 'small depressions 2l-e in the peripheral portions ofthe lingers 2 l-b, so spaced about the periphery as to 'register with and close the outer ends of the slots 2li-c in the member 20, as shown at the right of Figure 2.

The slots 20-6 of the member 20 may be substantially closed, to exclude coating liquid from between the contact surfacesy by means other than that shown 'in Figures l and `2. Thus, in Figures 3, 4 and 5 there is shown an alternative closure means applied to a rectier which is in all other respects substantially identical with that just described. However, in lieu of a pair of similar conducting members, such as the members 20 and 2I of Figures 1 and 2, in this embodiment of the invention a conducting member 22 is provided, similar in shape to the member 20, and having an upwardly dished central portion 22--a and radial fingers 22-b separated by radial slots 22-c. In order to substantially close the slots 22-c, a second conducting member 23 is interposed between the member 22 and the front electrode 3. The member 23 is flat throughout substantially its entire area except for a series of upwardly projecting ribs 23-a, they angular spacing of which corresponds to that of the slots 22--c in the member 22 so that the ribs may register with and project upwardly into the slots.

As shown in Figures 3 and 4, the ribs 23-a project upwardly a substantial distance, so that particularly noted with' reference to Figure iv that the ribs are generally triangular in transverse section, with downwardly diverging side walls. The reason for this will be apparent when it is realized that the greater the degree of flexing of the lingers 22-b toward the plane of the dished central portion ZZ-a, the wider the slots 22c become. Thus, by providing ribs 23-a with sides d-iverging downwardly at the proper angle, the width of the ribs is increased commensurate with the increase in width of the `slots 22--0 for corresponding adjusted heights of the central portion 22--a. The clearance between the side walls of the ribs 23-a and the sides of the slots 22--c Y is accordingly maintained substantially constant. This clearance may be so slight that surface tension of the -coating liquid will prevent its penetration therethrough.

The member 23 need not be oi resilient material since no flexing thereof is required, but in order to insure uniform pressure and uniform electrical contact between it and the electrode 3, radial slots 23-b may be provided therein (Figure 5) in staggered relation to the slots 22--c in the member 22. The slots 23-b are, of course, closed by the overlying fingers 22-b of the member 22.

A still further modified form of the invention is illustrated in Figures 6 and '7. In this embodiment the rectilier is substantially identical with that shown in the two previously described forms except for the specific manner by which the slots in the conducting member are closed against entry of coating liquid. The conducting member 30 is similar in shape to the members 20 and 22 of Figures 2 and 3, respectively, and comprises an upwardly dished central portion Sli-a and radially extending fingers Bilb separated by radial slots '3U-c. The slots 3ic in this instance are substantially closed by a series of upwardly extending `ribs or projections 3| formed integral with the front electrode 3. Thus, this form of the invention is, in substance, a modification of that shown in Figures 3, 4 and 5 by making the member 23 integral with the front electrode 3. Because of the similarity in all other respects between these two embodiments of the invention, further detailed description of Figures 6 and 7 is deemed unnecessary.

From the foregoing description of several forms which the invention may assume, it will be apparent that simple and effective means have been provided for preventing impairment of the electrical contact between the front electrode and the fingers of a resilient, slotted conducting member of a dry plate rectifier, when the rectifier is coated with a liquid coating material after assembly. It will also be apparent that this result is attained without `affecting the resilience of the conducting member and without in any other way affecting the performance of the rectifier or altering the relationship of the parts thereof.

We claim:

1. A rectifier structure comprising a base plate, a front electrode, a conducting member having means forming with said electrode a pocket, relatively movable spaced elements extending from said means for resiliently contacting said electrode, the spaces between said elements forming the sole openings into said pocket, and means for substantially closing said openings.

2. A rectifier structure comprising a base plate, a front electrode, a conducting `member having a plurality of generally radially disposed spaced fingers for resiliently engaging said electrode, and a second member also having a plurality of radially disposed spaced fingers and mounted with the fingers of the second member overlying the .spaces between the fingers of the first member to substantially close the spaces between the said fingers of the first member.

3. A rectifier structure comprising a base plate, a iront electrode, a conducting member having a plurality of generally radially disposed spaced fingers for resiliently engaging said electrode, a second member also having a plurality of radially disposed spaced fingers and'mounted with the fingers of the second member overlying the spaces between the fingers of the first member, as well as spaced peripheral projections adapted to enter the ends of said spaces, whereby tosubstantially close said spaces.

4. In a rectifier structure, a base plate, a front electrode, and a conducting member contacting said electrode, said member having relatively movable spaced elements for imparting resilience to the member, means forming a cover over the side of said member which is opposite the front electrode, to close the spaces between said elements, and a protective coating covering the rectifier structure.

5. In a rectifier structure, a base plate, a front electrode, a conducting member cooperating with said electrode, said member having a center portion forming with said electrode, a pocket, and a plurality of spaced fingers extending from said center portion for resiliently engaging said electrode, the spaces between said fingers'forming the sole openings into said pocket, and means forming projections on said front electrode for substantially .closing said openings.

6. A rectifier structure comprising a base plate, a front electrode, a conducting member cooperating with said electrode, said member having a raised center portion forming, with said electrode, a pocket, as well as a plurality of spaced fingers extending from said center portion for resiliently engaging said electrode, the spaces between said fingers forming the sole openings into said pocket, and a second member also having a raised center portion and spaced fingers extending therefrom, said second member being disposed in nested relationship with the first mentioned member, the fingers of the second member overlying the spaces between the fingers of the first member whereby the said openings are substantially closed.

'7. A rectifier structure comprising a base plate, a front electrode, a conducting member cooperating with said electrode, said member having a center portion forming, with said electrode, a pocket, as well as a plurality of spaced fingers extending from the center portion for resilientltr engaging said electrode, the spaces between said Fingers forming the sole openings into said pocket, and a member interposed between said conducting member and said electrode and having projections adapted to enter said spaces, whereby to substantially close said openings.

8. In a rectifier structure, a base plate, a front electrode, a rectifying layer between the base plate and the front electrode, a conducting member contacting said front electrode, said member having independently movable spaced resilient elements imparting resilience to the member, said front electrode having projections proportioned and spaced to protrude between the spaces between said elements to close said spaces.

9. A rectifier structure comprising a base plate, a iront electrode, a rectifying layer between the base plate and the front electrode, a conducting member having means forming with said electrode a pocket, independently movable spaced elements extending from said means for resiliently contacting said electrode, the spaces between said elements forming the sole openings into said pocket, means for substantially closing said openings, and a protective coating covering said conducting member and both of said means.

10. A rectier structure comprising a base plate, a front electrode, a rectifying layer between the base plate and the front electrode, a conducting member having a plurality of generally radially disposed spaced fingers resiliently engaging said electrode, a second member also having a plurality of radially disposed spaced fingers and mounted with the fingers of the second member overlying the spaces between the fingers of the first member to substantially close the spaces between said fingers of the rst member, and a protective coating covering and adhering to the exterior of the rectifier structure.

- ERIC LIDOW.

EDGAR M. BURLIN.

REFERENCES CITED UNITED STATES PATENTS Name Date Kipphan Oct. 25, 1938 Number 

